There will come a time when Bitcoin mining ends; per the Bitcoin Protocol, the number of Bitcoin will be capped at 21 million. What a Bitcoin miner does is analogous to that-they check transactions to make sure that users have not illegitimately tried to spend the same Bitcoin twice. If you want to estimate how much Bitcoin you could mine with your mining rig's hash rate, the site Cryptocompare offers a helpful calculator. You'd have to get a fast mining rig or, more realistically, join a mining pool-a group of miners who combine their computing power and split the mined bitcoin.